CN111185168B - Nano gold catalyst, preparation and application thereof - Google Patents
Nano gold catalyst, preparation and application thereof Download PDFInfo
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- CN111185168B CN111185168B CN202010038260.3A CN202010038260A CN111185168B CN 111185168 B CN111185168 B CN 111185168B CN 202010038260 A CN202010038260 A CN 202010038260A CN 111185168 B CN111185168 B CN 111185168B
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/66—Silver or gold
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
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- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/08—Preparation of carboxylic acid esters by reacting carboxylic acids or symmetrical anhydrides with the hydroxy or O-metal group of organic compounds
Abstract
The invention provides a nano gold catalyst, and preparation and application thereof. The preparation method of the nano-gold catalyst comprises the following steps of 1) reacting a metal oxide composite carrier containing silicon and aluminum with a silane coupling agent in a solvent to prepare a silane modified metal oxide composite carrier; 2) Carrying out polymerization reaction on the silane-modified metal oxide composite carrier and a hyperbranched polymer monomer to prepare a hyperbranched polymer-metal oxide composite carrier; and 3) reacting the hyperbranched polymer-metal oxide composite carrier with an active center or an active center precursor, and calcining the obtained solid to obtain the catalyst.
Description
Technical Field
The invention belongs to the technical field of catalysis, and particularly relates to a nanogold catalyst, preparation and application thereof, and an intermediate for preparing the catalyst.
Background
Methyl Methacrylate (MMA) is an important bridging monomer for connecting and synthesizing chemical engineering and polymer materials, has very wide application, and can be used for preparing organic glass, water-based paint, synthetic resin, functional polymer materials and the like.
The industrial production of MMA is currently dominated by the acetone cyanohydrin process (ACH process) and the isobutene process (i-C4 process). Among them, the acetone cyanohydrin method accounts for 83% of the global productivity, and the isobutylene method accounts for 16%. The ACH method uses virulent hydrocyanic acid and acetone as raw materials and highly corrosive sulfuric acid and caustic soda as auxiliary materials to generate a large amount of ammonium bisulfate byproducts, so that the atom utilization rate is low, equipment is seriously corroded, and the environment is greatly polluted.
Compared with the ACH method, the i-C4 method has the advantages that abundant C4 fraction is used as a raw material, the reaction process is environment-friendly, only water is used as a byproduct, and the atom utilization rate is high, so that the method becomes a development trend in recent years. The i-C4 process is further classified into a direct oxidation process (three-step process) and a direct methyl ester process (two-step process). The three-step method is a traditional process, and is firstly industrialized by Mitsubishi rayon company, namely isobutene is firstly oxidized into methacrolein under a molybdenum-based catalyst, the methacrolein is then oxidized into methacrylic acid, and the methacrylic acid is then esterified with methanol to obtain MMA. Compared with the method, the two-step method is developed by Asahi formation and is the earliest to realize industrialization in 1996, methylacrolein and methanol are directly oxidized and esterified in one step to obtain MMA, the process flow is shortened, and the energy consumption is reduced, so that the investment cost and the operation cost are greatly reduced, and the method has great economic significance.
The core of the direct methyl ester process (two-step process) lies in the preparation of the catalyst, the development of the catalyst goes through the process of improved heteropoly acid type catalysts, platinum-based, ruthenium-based, palladium-based catalysts, gold-based and other precious metal catalysts, wherein the palladium-based (Pd-Pb) developed by Asahi Kasei corporation successfully realizes the two-step conversion, compared with the three-step process, the process has high product purity, simple process equipment and low construction cost, but the Pd-Pb catalyst has the problems of low MMA selectivity (about 84%) and increased subsequent separation cost. On the basis, the Asahi Kasei corporation developed a nano gold catalyst (Au @ NiOx) with a core-shell structure, and the catalyst has excellent activity, selectivity and stability, and when the conversion rate of methacrolein is 65%, the selectivity of MMA is about 95%. However, the nanogold catalyst has high requirements on preparation technology, and the effective utilization rate (loading rate) of Au is only about 70%, so that the cost is high, and the industrial application of the nanogold catalyst is limited to a certain extent.
Chinese patent CN 107034A reports a catalyst comprising gold, silicon oxide, aluminium oxide and one or more oxides of elements selected from the group consisting of: li, na, K, rb, cs, be, mg, ca, sr, ba, sc, Y, ti, zr, cu, mn, pb, sn, bi or lanthanides having an atomic number of 57 to 71, which solves the problem of the water resistance of the catalyst. The patent synthesizes a catalyst with a shell structure, which has high activity, selectivity, hydrolytic stability and long service life by controlling conditions. However, since gold is still supported by the immersion method in this patent, the effective Au supporting rate is only about 70%, which is expensive.
Chinese patents CN109331839A, CN109395732 and CN109569600A respectively prepare the catalyst for preparing methyl methacrylate by selecting different active centers (gold and a lanthanide metal and a transition metal, gold and a rare earth metal, gold and two lanthanide metals) and applying a polymer protection method. The method comprises the steps of fully mixing a gold precursor, a reducing agent and deionized water under the stirring condition to obtain stable and high-dispersion gold sol, sequentially adding a promoter precursor and a carrier in the presence of a high-molecular protective agent, standing, filtering, drying and calcining after the reaction is finished to obtain the catalyst, wherein the selected high-molecular protective agent is polyvinyl alcohol, polyvinylpyrrolidone, tetrakis (hydroxymethyl) phosphonium chloride, polydimethyl-dipropenyl ammonium chloride, sodium citrate and thiol substances. Although the catalyst is simple to prepare, has excellent activity and stability, and the Au loading rate can reach 100%, the production cost is effectively reduced, the selected macromolecular protective agent is a straight-chain polymer or a micromolecular substance, the wrapping property of the macromolecular protective agent on gold particles in gold sol is poor, and the aggregation of gold cannot be effectively prevented. Therefore, in order to improve the encapsulation of gold particles in the gold sol, the usage amount of the polymeric protective agent (the mass ratio of the polymeric protective agent to the chloroauric acid is more than 1) must be increased, and the industrial application is limited. Meanwhile, the macromolecule protection method is to prepare the catalyst by generating gold sol and then loading the gold sol on a carrier, so that the concentration of a gold source in an aqueous solution is limited, and only a gold-based catalyst with low loading capacity can be prepared.
Compared with the traditional linear macromolecular polymer, the hyperbranched polymer is always a research hotspot in the field of macromolecules in the last 90 years, on one hand, the type and the number of functional groups in the molecule are accurately controllable, the molecular weight has polydispersity, the molecular configuration is an irregular ellipsoidal three-dimensional space structure, the molecular structure is highly branched like a tree, the interior of the molecular structure is provided with unique nano micropores, and the surface of the molecular structure contains a large number of functional groups, so that the embedding and the adsorption of metal and ions thereof are easily realized. On the other hand, the hyperbranched polymer can realize one-pot method (one-step) synthesis, generally does not need to be separated and purified step by step, and has simple process and lower cost. The characteristics make the compound has potential application value in a plurality of fields, and become a research hotspot in related fields. For example: the hyperbranched polyamide-amine polymer contains a large number of amino functional groups (primary amine, tertiary amine, amide and the like), the functional groups are increased in a geometric series along with the increase of molecular algebra, the inner layer contains a large number of cavities, and the surface contains a large number of polar groups, so that the hyperbranched polyamide-amine polymer is very soluble in water, and can be used as a large-capacity chelating agent for metal ions in an aqueous solution.
The silica gel has relatively good mechanical strength, easily controlled pore structure and specific surface area, contains abundant silicon hydroxyl on the surface, and can be subjected to surface physical and chemical modification. Chinese patent CN102161758A chemically bonds hyperbranched macromolecules to the surface of a silica gel solid to form a hyperbranched polymer chelate material, and the material has the dual characteristics of the hyperbranched macromolecules and the silica gel, so that the material has a good effect in the fields of heavy metal adsorption and separation. However, if silica gel is used as a carrier, the silica gel will gradually dissolve under repeated exposure to acid and alkali, resulting in the reduction of catalyst activity until deactivation, so that it is necessary to search for a new high-stability carrier graft-modified hyperbranched polymer, and further search for excellent properties of the synthesized catalyst.
In summary, the preparation of the catalyst for direct methyl ester process by obtaining MMA from methacrolein and methanol through one-step oxidative esterification still has the following problems:
1) The reported impregnation method has the problems of high technical requirement, low Au effective loading rate (about 70-90%), high cost and the like, and the obtained catalyst has low selectivity and activity.
2) In the reported polymer protection method, the polymer protective agent is a linear polymer or a small molecular substance, and the method has poor wrapping property on gold particles in gold sol, and the amount of the protective agent used is large (polymer protective agent: the mass ratio of the chloroauric acid is more than 1), the concentration of the gold source in the loaded mother liquor is low, and the like.
Therefore, there is still a need in the art for a highly active and stable nanogold catalyst and a preparation method thereof, which can improve the effective loading rate of gold, reduce the cost of the catalyst and/or improve the activity of the catalyst.
The invention content is as follows:
based on the defects of the prior art, the invention provides the nano-gold catalyst and the preparation method and application thereof, and the obtained catalyst has the advantages of good dispersion degree of active components, high activity, good stability and the like. The preparation process of the catalyst is simple, a reducing agent is not required to be added, the effective loading rate of the active component Au and the auxiliary active component is high, the waste of precious metals in the mother liquor is reduced, the cost is low, and the catalyst is suitable for industrial production.
In a first aspect of the present invention, there is provided a method for preparing a nanogold catalyst, comprising:
1) Reacting a metal oxide composite carrier containing silicon and aluminum with a silane coupling agent in a solvent to prepare a silane modified metal oxide composite carrier;
2) Carrying out polymerization reaction on the silane modified metal oxide composite carrier and a hyperbranched polymer monomer to prepare a hyperbranched polymer-metal oxide composite carrier;
3) And (3) reacting the hyperbranched polymer-metal oxide composite carrier with an active center or an active center precursor, and calcining the obtained solid to obtain the catalyst.
In a second aspect of the present invention, there is provided a nanogold catalyst prepared by a method comprising the steps of:
1) Reacting a metal oxide composite carrier containing silicon and aluminum with a silane coupling agent in a solvent to prepare a silane modified metal oxide composite carrier;
2) Carrying out polymerization reaction on the silane modified metal oxide composite carrier and a hyperbranched polymer monomer to prepare a hyperbranched polymer-metal oxide composite carrier;
3) And (3) reacting the hyperbranched polymer-metal oxide composite carrier with an active center or an active center precursor, and calcining the obtained solid to obtain the catalyst.
In a third aspect of the present invention, there is provided a method for producing a (meth) acrylate, comprising:
adding the nano gold catalyst into the mixture of (methyl) acrolein and alcohol, and introducing oxygen to carry out one-step oxidation esterification reaction to obtain the (methyl) acrylic ester.
In a fourth aspect of the present invention, there is provided an intermediate for preparing a nanogold catalyst, comprising a hyperbranched polymer-metal oxide composite support, and an active center or an active center precursor supported on the support, wherein the hyperbranched polymer molecule is bonded to the metal oxide composite support; the metal oxide composite carrier is a silane modified metal oxide composite carrier containing silicon and aluminum.
In a fifth aspect of the invention, there is provided a use of a nanogold catalyst in the preparation of methyl methacrylate.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments, but the scope of the present invention includes, but is not limited to, the following examples, and any modifications made to the details and form of the technical solution of the present invention may fall within the scope of the present invention without departing from the meaning and scope of the present application.
Herein, "(meth) acrylate" refers to acrylate, methacrylate, or a mixture thereof; "(meth) acrolein" means acrolein, methacrolein, or a mixture thereof.
The preparation method of the nano gold catalyst comprises the following steps:
step 1) reacting the metal oxide composite carrier containing silicon and aluminum with a silane coupling agent in a solvent to prepare the silane modified metal oxide composite carrier.
Preferably, said step 1) is carried out under heated conditions. Preferably, the heating conditions are from 50 to 150 ℃, more preferably from 100 to 140 ℃, most preferably from 110 to 130 ℃.
Preferably, in step 1), the silane coupling agent is selected from one or more of an amino-functional group-containing silane coupling agent, a mercapto-functional group-containing silane coupling agent, a hydroxyl-functional group-containing silane coupling agent, such as aminopropyltrialkoxysilane, mercaptopropyltrialkoxysilane, diethylenetriaminotrialkoxysilane, and the like.
Preferably, in step 1), the composite support of metal oxide containing silicon and aluminum is a composition formed by silica, alumina and other metal oxides selected from one or more of alkali metal oxides, alkaline earth metal oxides, tiO2, ceO, zrO2, spinel, hydrotalcite, coOx (x = 0.5-2.5), niOy (y = 0.5-2.5). Preferably, the silicon-aluminum-containing metal oxide composite carrier contains 65-98 wt% of SiO2 and 1-35 wt% of Al2O3 based on the total weight of the silicon-aluminum-containing metal oxide composite carrier; 1-20 wt.% of other metal oxides.
Preferably, the preparation process of the metal oxide composite carrier containing silicon and aluminum in step 1) is as follows: under the condition of stirring, fully mixing a silicon dioxide precursor, an aluminum oxide precursor and other metal precursors, adding acid to adjust the pH value of the mixed solution to 0.5-1.4, continuously stirring and curing for 1-24h to obtain a mixture, spray drying and molding the mixture to obtain spherical particles of 10-200 mu m, and calcining in air or inert atmosphere to obtain the metal oxide composite carrier.
Preferably, the acid used to adjust the pH is selected from one or more of an inorganic or organic acid, such as nitric acid, hydrochloric acid, formic acid, acetic acid.
Preferably, the precursor of the silicon dioxide is selected from silica sol, solid silica gel and white carbon black; the precursor of the aluminum oxide is selected from aluminum nitrate, aluminum chloride, aluminum hydroxide, aluminum phosphate, aluminum sulfate and aluminum oxide powder; the other metal precursor is one or more of nitrate, oxide, hydroxide, compound or other compounds of corresponding metal, and the other compounds refer to special metal salt precursors of some metals, such as zirconium oxychloride as a precursor of zirconium dioxide, titanyl sulfate as a precursor of titanium dioxide, cerium oxalate as a precursor of cerium dioxide, and the like.
Preferably, the solvent used in step 1) is an organic solvent, preferably the solvent is toluene, xylene or benzene.
More preferably, the specific steps of step 1) are as follows: mixing the metal oxide composite carrier containing silicon and aluminum with a silane coupling agent, dissolving the mixture in toluene, and stirring and reacting at 50-150 ℃ for 2-12h to obtain the silane modified metal oxide composite carrier.
The method also comprises the step 2) of carrying out polymerization reaction on the silane modified metal oxide composite carrier and a hyperbranched polymer monomer to prepare the hyperbranched polymer-metal oxide composite carrier.
Preferably, the step 2) is carried out under heating and reduced pressure, preferably, the heating condition is 60 to 150 ℃, more preferably 70 to 120 ℃, and the reduced pressure condition is 0Pa to 200Pa, preferably 0Pa to 160Pa, more preferably 0Pa to 120Pa.
Preferably, in step 2), the monomers used to form the hyperbranched polymer are prepared by: and carrying out Michael addition reaction on polyamine and alpha, beta unsaturated carbonyl compound to prepare a monomer for forming the hyperbranched polymer.
Preferably, the polyamine is selected from diamine, triamine and tetraamine, and may be one or more of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, diethylenetriamine or triethylenetetramine. The alpha, beta unsaturated carbonyl compound is one or more of alkyl acrylate and alkyl methacrylate, preferably one or more of C1-6 alkyl acrylate and C1-6 alkyl methacrylate, such as methyl acrylate or methyl methacrylate. The solvent used in the monomer reaction for forming the hyperbranched polymer is one or more of methanol, ethanol, tetrahydrofuran and isopropanol.
More specifically, the preparation steps of the monomers used to form the hyperbranched polymer are: sequentially adding a certain amount of polyamine and a certain amount of solvent (the volume ratio of the polyamine to the solvent is 1-1.
More preferably, the specific steps of step 2) are as follows: adding the silane modified metal oxide composite carrier prepared in the step 1) into a reaction container, slowly dropwise adding a monomer of the hyperbranched polymer within 0.5-6h, and stirring and reacting at 60-150 ℃ and 40-120 Pa for 3-15h to prepare the hyperbranched polymer-metal oxide composite carrier.
The method also comprises the step 3) of reacting the hyperbranched polymer-metal oxide composite carrier with an active center or an active center precursor, and calcining the obtained solid to obtain the catalyst.
Preferably, said step 3) is carried out under heating conditions ranging from 30 to 150 ℃, preferably from 60 to 120 ℃. Preferably, the reaction time is 10min-12h,0.5-10h, preferably 2h-8h.
Preferably, the active center in step 3) comprises an active component gold and a co-active component rare earth metal, and the co-active component rare earth metal is selected from one or more of Sc, Y, la, ce, pr, nd and Sm.
The loading amount of gold in the catalyst prepared by the method is 0.03-1.0wt%, the loading amount of rare earth metal is 0.005wt% -2.0wt%, and preferably, the rare earth metal is selected from one or more of Sc, Y, la, ce, pr, nd and Sm.
According to the method, the loading rate of the active component gold is 95% -100%.
Preferably, in step 3), the gold precursor is selected from one or more of aurous chloride, gold chloride, chloroauric acid, chloroaurate, aurous chlorohydrate (HAuCl 2), tetrabromoauric acid, tetrabromoaurate, potassium aurous cyanide or sodium gold sulfite; the precursor of the rare earth metal is one or two of nitrate and acetate of corresponding metal.
Preferably, the adding sequence of the materials in the step 3) is to add the hyperbranched polymer-metal oxide composite carrier, add the active center precursor mixed solution, and obtain the catalyst after filtering, drying and calcining.
More specifically, the step 3) comprises the following specific steps: adding the hyperbranched polymer-metal oxide composite carrier prepared in the step 2) into deionized water, stirring uniformly at 50-150 ℃, preferably 70-110 ℃, adding an active center precursor mixed solution, continuously stirring for reaction for 0.5-12h, filtering, washing the obtained solid with the deionized water for 2-10 times, washing with absolute ethyl alcohol for 1-3 times, drying, and calcining at 200-800 ℃, preferably 400-600 ℃ to obtain the catalyst. The mass ratio of the components is as follows, and the rare earth metals (based on the weight of the rare earth metals): gold (by weight of gold): hyperbranched polymer-based metal oxide composite support: the mass ratio of water is as follows: 1:0.02-1.43:60-250:100-800.
The nanogold catalyst of the invention is prepared by the method described above.
Preferably, the gold loading in the catalyst is from 0.03 to 1.0wt%, preferably from 0.1 to 0.8wt%, more preferably from 0.3 to 0.7wt%, most preferably from 0.4 to 0.6 wt%, most preferably from 0.45 to 0.5wt%. The loading of rare earth metal is 0.005wt% to 2.0wt%, preferably 0.008 wt% to 1wt%, more preferably 0.01 wt% to 0.7wt%, most preferably 0.015 wt% to 0.5wt%.
Preferably, in the nanogold catalyst, the auxiliary active component rare earth metal is selected from one or more of Sc, Y, la, ce, pr, nd and Sm.
The nanogold catalyst of the invention can be used for preparing (meth) acrylate, and the method for preparing (meth) acrylate comprises the following steps:
adding the nano gold catalyst into the mixture of (methyl) acrolein and alcohol, and introducing oxygen to carry out one-step oxidation esterification reaction to obtain (methyl) acrylic ester.
Preferably, the mixture of (meth) acrolein and alcohol further contains a polymerization inhibitor. The polymerization inhibitor is selected from one or more of hydroquinone, methyl hydroquinone, p-hydroxyanisole, tert-butyl catechol, phenothiazine, N-oxyl-4-hydroxy-2, 6-tetramethyl piperidine and tris (N-oxyl-2, 6-tetramethyl piperidine) phosphite.
Preferably, the molar ratio of the alcoholic hydroxyl group of the alcohol to the aldehyde group of (meth) acrolein is 1.
The alcohol may be a monohydric alcohol, such as methanol, ethanol, and the like.
Preferably, the conditions of the oxidative esterification reaction are: the reaction temperature is 40-100 ℃, preferably 65-95 ℃, the reaction pressure is 0.1-4MPa, and the reaction time is 0.5-8 h, preferably 2-4h.
The intermediate for preparing the nanogold catalyst comprises a hyperbranched polymer-metal oxide composite carrier and an active center or an active center precursor loaded on the carrier, wherein the hyperbranched polymer is molecularly bonded to the metal oxide composite carrier; the metal oxide composite carrier is a silane modified metal oxide composite carrier containing silicon and aluminum.
Preferably, the silane coupling agent is selected from one or more of an amino-functional group-containing silane coupling agent, a mercapto-functional group-containing silane coupling agent, a hydroxyl-functional group-containing silane coupling agent, such as aminopropyltrialkoxysilane, mercaptopropyltrialkoxysilane, diethylenetriaminotrialkoxysilane, and the like.
Preferably, the composite support of metal oxide containing silicon and aluminum is a composition formed by silica, alumina and other metal oxides selected from one or more of alkali metal oxides, alkaline earth metal oxides, tiO2, ceO, zrO2, spinel, hydrotalcite, coOx (x = 0.5-2.5), niOy (y = 0.5-2.5). Preferably, the silicon-aluminum-containing metal oxide composite carrier contains 65-98 wt% of SiO2 and 1-35 wt% of Al2O3 based on the total weight of the silicon-aluminum-containing metal oxide composite carrier; 1-20 wt.% of other metal oxides.
Preferably, the preparation process of the metal oxide composite carrier containing silicon and aluminum is as follows: under the condition of stirring, fully mixing a silicon dioxide precursor, an aluminum oxide precursor and other metal precursors, adding acid to adjust the pH value of the mixed solution to 0.5-1.4, continuously stirring and curing for 1-24h to obtain a mixture, spray drying and molding the mixture to obtain spherical particles of 10-200 mu m, and calcining in air or inert atmosphere to obtain the metal oxide composite carrier.
Preferably, the acid used to adjust the pH is selected from one or more of an inorganic or organic acid, such as nitric acid, hydrochloric acid, formic acid, acetic acid.
Preferably, the precursor of the silicon dioxide is selected from silica sol, solid silica gel and white carbon black; the precursor of the aluminum oxide is selected from aluminum nitrate, aluminum chloride, aluminum hydroxide, aluminum phosphate, aluminum sulfate and aluminum oxide powder; the other metal precursor is one or more of nitrate, oxide, hydroxide, compound or other form of compound of the corresponding metal. Other forms of compounds refer to specific metal salt precursors of some metals, such as zirconium oxychloride, a precursor of titanium dioxide, titanyl sulfate, a precursor of cerium dioxide, cerium oxalate, and the like.
The hyperbranched polymer molecules are bonded to the metal oxide composite support by: carrying out Michael addition reaction on polyamine and alpha, beta unsaturated carbonyl compounds to obtain monomers for preparing hyperbranched polymers, mixing the monomers with a silane modified metal oxide composite carrier, and carrying out in-situ polymerization to enable hyperbranched polymer molecules to be linked to the metal oxide composite carrier.
Preferably, the polyamine is selected from diamine, triamine and tetraamine, and may be one or more of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, diethylenetriamine or triethylenetetramine. The alpha, beta unsaturated carbonyl compound is one or more of alkyl acrylate and alkyl methacrylate, preferably one or more of C1-6 alkyl acrylate and C1-6 alkyl methacrylate, such as methyl acrylate or methyl methacrylate. The solvent used for the reaction of the monomers for forming the hyperbranched polymer is one or more of methanol, ethanol, tetrahydrofuran and isopropanol.
More specifically, the monomers used to prepare the hyperbranched polymer are prepared by the steps of: sequentially adding a certain amount of polyamine and a certain amount of solvent (the volume ratio of the polyamine to the solvent is 1-1 to 50) into a reaction kettle with mechanical stirring, quickly stirring at 20-120 ℃ after replacing by inert gas, slowly dropwise adding one or more alpha, beta unsaturated carbonyl compounds according to the proportion that the molar ratio of amino hydrogen to double bond is 50-500%, keeping the reaction temperature for 2-24 hours after the feeding is finished, and removing the solvent under reduced pressure to obtain a product.
Preferably, the active center comprises an active component gold and a co-active component rare earth metal; preferably, the auxiliary active component rare earth metal is selected from one or more of Sc, Y, la, ce, pr, nd and Sm.
The Au precursor is selected from one or more of aurous chloride, gold chloride, chloroauric acid salt, chlorohydraauric acid (HAuCl 2), tetrabromoauric acid salt, potassium aurous cyanide or sodium aurous sulfite; the precursor of the rare earth metal is one or two of nitrate and acetate of corresponding metal.
And washing, drying and calcining the intermediate to obtain the catalyst.
The invention has the beneficial effects that: the hyperbranched polymer molecule is linked to the metal oxide composite carrier containing silicon and aluminum, and the hyperbranched polymer chelating material carrier is prepared. And loading the active center on the carrier, and calcining to obtain the nano gold catalyst. The hyperbranched polymer chelating material carrier has wide application range to different auxiliary active components, not only maintains the stability of the silicon-aluminum containing metal oxide composite carrier, but also can play the chelating role of hyperbranched macromolecules. The hyperbranched polymer chelating material carrier not only maintains the stability of the silicon-aluminum-containing metal oxide composite carrier, but also can play a role in chelating macromolecules of hyperbranched polymers. Meanwhile, the three-dimensional space structure of the hyperbranched polymer can effectively prevent the aggregation of gold and the auxiliary active components, so that the nano particles are more dispersed, and the high-activity catalyst with the active nano particles between 1 nm and 5nm is obtained. The obtained nano gold catalyst is used in the reaction of preparing methyl methacrylate by one-step oxidation esterification, under the optimized condition, the conversion rate of methacrolein is more than or equal to 95%, the selectivity of methyl methacrylate is more than or equal to 98%, the catalyst continuously runs for 6 months, and the reaction activity basically keeps unchanged. Therefore, the obtained catalyst has the advantages of good dispersion degree of active components, high activity, good stability and the like. The preparation process is simple, a reducing agent is not required to be added, the effective loading rate of the active component Au and the auxiliary active component is high, the waste of noble metals in the mother liquor is reduced, the cost is low, and the preparation method is suitable for industrial production.
Example 1
1) Preparation of hyperbranched high-molecular polymer monomer A:
a100 mL three-necked flask equipped with a mechanical stirrer and a thermometer was charged with 2.70mL of diethylenetriamine (0.0251 mol) and 30mL of methanol, and after nitrogen substitution, 20mL of a methanol solution containing 9.00 mL of methyl acrylate (0.0993 mol) was slowly added dropwise from a constant dropping funnel over 1 hour at room temperature. The reaction was continued for 4h after the addition was complete and methanol was removed under reduced pressure to give the product as a clear yellow oil in >97% yield.
2) Preparation of alkoxysilane-modified metal oxide composite support
Mixing 10g of 30% silica sol (pH = 4.5), 7.5026g of aluminum nitrate nonahydrate, 0.8748g of magnesium hydroxide, 2.3097g of cerium nitrate, 2g of 75% concentrated nitric acid with mass concentration and 50mL of deionized water uniformly at 50 ℃, keeping the temperature, continuing stirring for 24 hours to obtain a uniform solid solution suspension, stirring to reduce the temperature to room temperature, and then spray-drying. Spray drying gave a spherical powder with a particle size of 58 μm. And (3) placing the solid powder in a tubular furnace, and calcining at 600 ℃ under nitrogen or air to obtain the Si-Mg-Al-Ce metal composite oxide carrier.
100g of Si-Mg-Al-Ce metal composite oxide carrier is placed in a 250mL single-neck flask, 20mL of 3-aminopropyltriethoxysilane and 50mL of toluene are sequentially added, and the reaction is carried out for 5 hours at the temperature of 120 ℃. And after filtering the product, washing the product for 2 to 3 times by using toluene and ethanol in sequence to obtain the metal oxide composite carrier modified by the alkoxy silane.
3) Hyperbranched polymer metal oxide composite carrier
Adding 50g of alkoxy silane modified metal oxide composite carrier into a 250mL single-neck flask, slowly dropwise adding hyperbranched polymer monomer A within 1h, and reacting for 6h under vacuum stirring at 80 ℃ and 120Pa to obtain the hyperbranched polymer metal oxide composite carrier.
4) Preparation of nano gold catalyst
Sequentially adding 96g of hyperbranched polymer metal oxide composite carrier and 100mL of deionized water into a reactor, uniformly mixing, stirring uniformly at 90 ℃, adding 60mL of active component mixed solution containing 1g of chloroauric acid and 1.525g of scandium nitrate, keeping the temperature, continuously stirring for 2h, cooling and filtering after the reaction is finished, sequentially washing with deionized water and ethanol, drying for 1h at 80 ℃, placing in a muffle furnace, and calcining at 500 ℃ to obtain the catalyst a (Au-Sc/Si-Mg-Al-Ce). In the ICP measurement, the mass percentage of Au and Sc in the catalyst is respectively 0.4796% and 0.2009%. The Au loading rate was 97.01%. The calculation method of the Au loading rate is as follows:
au loading rate Z% = m w _ 1/(m _ 0w _) × 100%
m total mass/g of catalyst obtained
w1 mass percent of Au in the catalyst
m0 mass/g of chloroauric acid added in the supported catalyst
w0 mass percent of Au in the chloroauric acid reagent%
Comparative example 1
Preparation of Metal oxide composite Carrier
Mixing 10g of 30% silica sol (pH = 4.5), 7.5026g of aluminum nitrate nonahydrate, 0.8748g of magnesium hydroxide, 2.3097g of cerium nitrate, 2g of 75% concentrated nitric acid with mass concentration and 50mL of deionized water at 50 ℃, keeping the temperature, continuously stirring for 24 hours to obtain a uniform solid solution suspension, and performing spray drying after stirring to reduce the temperature to room temperature. Spray drying gave a spherical powder with a particle size of 58 μm. And (3) putting the solid powder into a tubular furnace, and calcining at 600 ℃ under nitrogen or air to obtain the Si-Mg-Al-Ce metal composite oxide carrier.
Preparation of nano gold catalyst (impregnation method)
And sequentially adding 96g of the Si-Mg-Al-Ce metal composite oxide carrier and 100mL of deionized water into a reactor, uniformly mixing, stirring uniformly at 90 ℃, adding 60mL of active component mixed solution containing 1g of chloroauric acid and 1.525g of scandium nitrate, keeping the temperature, continuously stirring for 2h, cooling and filtering after the reaction is finished, sequentially washing with deionized water and ethanol, drying for 1h at 80 ℃, placing in a muffle furnace, and calcining at 500 ℃ to obtain the catalyst a' (Au-Sc/Si-Mg-Al-Ce). The mass percentage of Au and Sc in the catalyst is respectively 0.4184% and 0.1793% in ICP determination. The Au loading was 84.63%.
Comparative example 2
Preparation of Metal composite oxide support As in example 1
Mixing 10g of 30% silica sol (pH = 4.5), 7.5026g of aluminum nitrate nonahydrate, 0.8748g of magnesium hydroxide, 2.3097g of cerium nitrate, 2g of 75% concentrated nitric acid with mass concentration and 50mL of deionized water at 50 ℃, keeping the temperature, continuously stirring for 24 hours to obtain a uniform solid solution suspension, and performing spray drying after stirring to reduce the temperature to room temperature. Spray drying gave a spherical powder with a particle size of 58 μm. And (3) placing the solid powder in a tubular furnace, and calcining at 600 ℃ under nitrogen or air to obtain the Si-Mg-Al-Ce metal composite oxide carrier.
Preparation of nano gold catalyst (impregnation method)
And sequentially adding 96g of the Si-Mg-Al-Ce metal composite oxide carrier and 100mL of deionized water into a reactor, uniformly mixing, stirring uniformly at 90 ℃, adding 60mL of active component mixed solution containing 1g of chloroauric acid and 1.50g of lanthanum nitrate, keeping the temperature, continuously stirring for 2 hours, cooling and filtering after the reaction is finished, sequentially washing with deionized water and ethanol, drying for 1 hour at 80 ℃, placing in a muffle furnace, and calcining at 500 ℃ to obtain the catalyst e' (Au-La/Si-Mg-Al-Ce). The mass percentages of Au and La in the catalyst are respectively 0.4247% and 0.4176% by ICP determination. The Au loading was 86.15%.
Example 2
Hyperbranched polymer monomer was prepared under the same conditions as in example 1, wherein 2.70mL of diethylenetriamine (0.0251 mol) was replaced with 4.9mL of hexamethylenediamine (0.0376 mol), and the nanogold catalyst was prepared under the same conditions and in the same proportions as in example 1, to obtain catalyst b (Au-Sc/Si-Mg-Al-Ce). The mass percentage of Au and Sc in the catalyst is respectively 0.4746% and 0.1988% in ICP determination. The Au loading was 97.50%.
Example 3
Hyperbranched polymer monomers were prepared under the same conditions as in example 1, wherein 2.70mL of diethylenetriamine (0.0251 mol) was replaced with 5mL of ethylenediamine (0.0752 mol); during preparation of the nanogold catalyst, scandium nitrate was replaced with 0.10g of lanthanum nitrate, and the rest of the conditions were the same as in example 1 to obtain catalyst c (Au-La/Si-Mg-Al-Ce). The mass percentage of Au and La in the catalyst is respectively 0.4804% and 0.0319% in ICP measurement. The Au loading was 96.99%.
Example 4
The same procedures used in example 1 were repeated except that 2.3097g of cerium nitrate in the preparation step of the alkoxysilane-modified metal oxide composite carrier was replaced with 4.4g of zirconium nitrate to obtain catalyst d (Au-Sc/Si-Mg-Al-Zr). The mass percentages of Au and Sc in the catalyst are respectively 0.4824% and 0.2021% by ICP determination. The Au loading was 97.57%.
Example 5
The preparation conditions of the hyperbranched polymer metal oxide composite carrier are the same as those of example 1, and when the nanogold catalyst is prepared, 1.50g of lanthanum nitrate is used for replacing scandium nitrate to obtain a catalyst e (Au-La/Si-Mg-Al-Ce). The mass percentage of Au and La in the catalyst is respectively 0.4810% and 0.4812% in ICP measurement. The Au loading rate was 97.11%.
Example 6
The preparation conditions of the hyperbranched polymer metal oxide composite carrier are the same as those of example 1, and when the nanogold catalyst is prepared, scandium nitrate is replaced by 0.050g of lanthanum nitrate to obtain a catalyst f (Au-La/Si-Mg-Al-Ce). The mass percentages of Au and La in the catalyst are respectively 0.4856% and 0.0156% in ICP determination. The Au loading rate was 98.22%.
Example 7
The catalysts obtained in examples 1 to 6 were used for the preparation of methyl methacrylate by one-step oxidative esterification under the same conditions as follows:
the catalyst of the invention is added into a reaction kettle, so that the molar ratio of gold/methacrolein in the catalyst system is 1. Uniformly mixing methacrolein and methanol according to a molar ratio of 1. The reaction temperature is 80 ℃, the product after the reaction is discharged at the rate which is the same as the feeding rate of the reaction raw material, the feed liquid is taken out at regular intervals, the tertiary amyl alcohol is added as an internal standard substance, and the reaction result is analyzed by using a Gas Chromatography (GC). The conversion of methacrolein and the selectivity of methyl methacrylate at 1000h and 2000h of reaction were calculated, respectively.
Comparing examples 1-6 with comparative examples 1 and 2 in the table, the nano gold catalyst can keep higher activity and selectivity for a long time, especially 2000h, under the premise of improving the effective loading rate of the active component. The hyperbranched polymer is introduced into the carrier, and the three-dimensional space structure of the hyperbranched polymer can effectively prevent the aggregation of gold and the auxiliary active component, so that the nano particles are more dispersed, and the activity of the catalyst is improved.
Claims (20)
1. A method of preparing a nanogold catalyst, comprising:
1) Reacting a metal oxide composite carrier containing silicon and aluminum with a silane coupling agent in a solvent to prepare a silane modified metal oxide composite carrier;
2) Carrying out polymerization reaction on the silane-modified metal oxide composite carrier and a hyperbranched polymer monomer to prepare a hyperbranched polymer-metal oxide composite carrier; and
3) Reacting the hyperbranched polymer-metal oxide composite carrier with an active center or an active center precursor, and calcining the obtained solid to obtain the catalyst;
in step 2), the monomers used to form the hyperbranched polymer are prepared by: carrying out Michael addition reaction on polyamine and an alpha, beta unsaturated carbonyl compound to prepare a monomer for forming the hyperbranched polymer;
in the step 3), the active center comprises an active component gold and an auxiliary active component rare earth metal, and the auxiliary active component rare earth metal is selected from one or more of Sc, Y, la, ce, pr, nd and Sm.
2. The method according to claim 1, wherein in step 1), the silane coupling agent is selected from one or more of an amino-functional group-containing silane coupling agent, a mercapto-functional group-containing silane coupling agent, and a hydroxyl-functional group-containing silane coupling agent.
3. The method of claim 1, wherein in step 1), the silane coupling agent is selected from one or more of aminopropyltrialkoxysilane, mercaptopropyltrialkoxysilane, divinyltriaminotrialkoxysilane.
4. The method of claim 1, wherein in step 1), the silica-alumina containing metal oxide composite support is a combination of silica, alumina and other metal oxides selected from the group consisting of alkali metal oxides, alkaline earth metal oxides, tiO 2 、CeO、ZrO 2 Spinel, hydrotalcite, coO x 、NiO y Wherein x =0.5-2.5 and y =0.5-2.5.
5. The method of claim 1, wherein the polyamine is selected from one or more of a diamine, a triamine, and a tetramine; the alpha, beta unsaturated carbonyl compound is one or more of alkyl acrylate and alkyl methacrylate.
6. The method of claim 1, wherein the polyamine is selected from one or more of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, diethylenetriamine, or triethylenetetramine.
7. A nanogold catalyst produced by the method of any one of claims 1 to 6.
8. The nanogold catalyst of claim 7, wherein the gold loading in the catalyst is between 0.03 and 1.0wt% and the rare earth metal loading is between 0.005wt% and 2.0wt%.
9. A method in the preparation of methyl (meth) acrylate comprising:
adding the nano gold catalyst of claim 7 into a mixture of (meth) acrolein and alcohol, and introducing oxygen to perform a one-step oxidative esterification reaction to obtain (meth) acrylic ester.
10. The method according to claim 9, wherein the mixture of (meth) acrolein and alcohol further contains a polymerization inhibitor.
11. The method of claim 10, wherein the polymerization inhibitor is one or more selected from hydroquinone, methyl hydroquinone, p-hydroxyanisole, t-butyl catechol, phenothiazine, N-oxyl-4-hydroxy-2, 6-tetramethyl piperidine and tris (N-oxyl-2, 6-tetramethyl piperidine) phosphite.
12. An intermediate for preparing a nanogold catalyst, comprising a hyperbranched polymer-metal oxide composite support and an active center or an active center precursor supported on the support, wherein the hyperbranched polymer is molecularly bonded to the metal oxide composite support; the metal oxide composite carrier is a silicon-aluminum-containing metal oxide composite carrier subjected to silane modification by using a silane coupling agent;
the monomers used to form the hyperbranched polymer are prepared by: carrying out Michael addition reaction on polyamine and an alpha, beta unsaturated carbonyl compound to prepare a monomer for forming the hyperbranched polymer;
the active center comprises an active component gold and an auxiliary active component rare earth metal; the auxiliary active component rare earth metal is selected from one or more of Sc, Y, la, ce, pr, nd and Sm.
13. The intermediate of claim 12, wherein the silane coupling agent is selected from one or more of an amino-functional silane coupling agent, a mercapto-functional silane coupling agent, and a hydroxyl-functional silane coupling agent.
14. The intermediate of claim 12, wherein said silane coupling agent is selected from one or more of aminopropyltrialkoxysilane, mercaptopropyltrialkoxysilane, and divinyltriaminotrialkoxysilane.
15. The intermediate of claim 12, wherein the silica-alumina containing metal oxide composite support is a combination of silica, alumina and other metal oxides selected from the group consisting of alkali metal oxides, alkaline earth metal oxides, tiO 2 、CeO、ZrO 2 Spinel, hydrotalcite and CoO x 、NiO y Wherein x =0.5-2.5, y =0.5-2.5.
16. The intermediate of claim 12, wherein the silicon-aluminum containing metal oxide composite support comprises from 65 to 98 weight percent SiO, based on the total weight of the silicon-aluminum containing metal oxide composite support 2 1-35% by weight of Al 2 O 3 (ii) a 1-20 wt.% of other metal oxides.
17. The intermediate of claim 12, wherein the silicon aluminum containing metal oxide composite support is prepared by: under the condition of stirring, fully mixing a silicon dioxide precursor, an aluminum oxide precursor and other metal precursors, adding acid to adjust the pH value of the mixed solution to 0.5-1.4, continuously stirring and curing for 1-24h to obtain a mixture, spray drying and molding the mixture to obtain spherical particles of 10-200 mu m, and calcining in air or inert atmosphere to obtain the metal oxide composite carrier.
18. The intermediate of claim 12, wherein the hyperbranched polymer molecules are bonded to the metal oxide composite support by: carrying out Michael addition reaction on polyamine and an alpha, beta unsaturated carbonyl compound to obtain a monomer for preparing a hyperbranched polymer, mixing the monomer with a silane modified metal oxide composite carrier containing silicon and aluminum, and carrying out in-situ polymerization to bond hyperbranched polymer molecules to the metal oxide composite carrier.
19. The intermediate of claim 12, wherein the polyamine is selected from the group consisting of diamines, triamines, and tetraamines, such as one or more of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, diethylenetriamine, and triethylenetetramine, and the α, β unsaturated carbonyl compound is one or more of alkyl acrylate, alkyl methacrylate; the solvent used in the reaction is one or more of methanol, ethanol, tetrahydrofuran and isopropanol.
20. The intermediate of claim 12, wherein the gold precursor is selected from the group consisting of aurous chloride, gold chloride, chloroauric acid salts, and aurous chlorohydrohydrogen acid (HAuCl) 2 ) One or more of tetrabromoauric acid, tetrabromoaurate, potassium aurous cyanide or sodium gold sulfite; the precursor of the rare earth metal is one or two of nitrate and acetate of corresponding metal.
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